A system for percussion rock drilling is previously known, wherein the individual drill string component includes a striker rod that transmits stress wave or shock wave energy and feed force from the drill rig and the rock drilling machine (hammer) to the drill bit. Basically, in a drill string including a plurality of drill string components of the type intended here, the striker rods make contact with each other and the shock wave propagates through the lengths of the striker rods and over the contact surfaces between the striker rods.
The individual drill string component also includes a tube-shaped, rotation force transmitting unit having screw threads at each end for joining it to other drill string components. A most distal element of the drill string for receiving the drill bit is named drill head.
The striker rod is coaxial with and extends inside the tube-shaped unit. A limited relative axial movement is allowed between the striker rod and the tube-shaped unit allowing the minor necessary displacements of the striker rod in respect to the tube-shaped unit during propagation of the stress wave to be unrestricted. An important function of the drill string component is to allow transportation of flushing fluid which in this case normally is pressurized air together with suspended lubricant droplets.
The flushing fluid has the function to provide for removal of disintegrated rock and to provide lubrication between relatively moveable parts of the components of the system.
The previously known system functions well, and in comparison to commonly known older one-piece threaded drill string components, it offers better efficiency and reduced losses in transferring the stress wave from the hammer to the drill bit. The reason for this is that the stress wave is transferred between contact surfaces being essentially planar end surfaces on the striker rods as a contrast to threaded joints of the older components.
The present invention addresses issues regarding further development of the above drill hit such as possibility to provide increased working life of the different parts, enhanced economy and operational security.
A system according to the background art is marketed by the Applicant under the trade name “Coprod”.
US2008/0078584 A1 describes a drill bit assembly for a down the hole hammer, wherein the bit has a plurality of axially extending bit lugs for co-operation with a corresponding plurality of axially extending chuck lugs on a holding chuck.